The purpose of this project is to characterize the cancer experience of populations with altered immune status. Risks of cancer of different sites are quantified for various groups of such patients, compared with each other and with national rates, and characteristics and possible determinants of unusual risks are sought. The populations studied include renal transplant recipients, kidney dialysis patients, patients with inherited and acquired immunologic disorders, and groups of immunostimulated persons. Evidence from these studies suggests that some immune factors, while apparently not of major relevance to some tumors, are important in the development of certain others, particularly non-Hodgkin's lymphoma.